The World Health Organization (WHO) has changed its advice on face masks, saying they should be worn in public to help stop the spread of coronavirus.
The global body said new information showed they could provide "a barrier for potentially infectious droplets".
Some countries around the world already recommend or mandate the wearing of face coverings in public.
The WHO had previously argued there was not enough evidence to say that healthy people should wear masks.
Dr Maria Van Kerkhove, the WHO's technical lead expert on Covid-19, told Reuters news agency the recommendation was for people to wear a "fabric mask - that is, a non-medical mask".
It was blatantly obvious to many at the very beginning of the outbreak.
The simple face mask is probably a major reason why countries in Asia have relatively lower rates of infection compared to those elsewhere.